This project consists of the research and development of a unique implantable ischemia monitor that uses subcutaneous sensors in the patient's torso to detect the onset of acute myocardial infarction (AMI). Upon detecting a heart attack, the monitor generates an alarm, which enables the patient to promptly seek medical treatment. In the United States, the median symptom-to-hospital time is 2.4 hours. Lengthy delays between symptom onset and a patient's arrival at a hospital cause both substantial heart tissue damage and many deaths. Approximately 50% of heart attack patients have either atypical or no symptoms at all, causing significant delays in treatment. Each 30 minute reduction of treatment delay provides a 7.5% decrease in mortality and 8.7% decrease in the incidence of congestive heart failure. Prompt treatment of AMIs enabled by real-time ischemia monitoring and alerting will save lives and decrease morbidity. In 2010, approximately 1.4 million people in the United States will have heart attacks, and approximately 400,000 of these victims will die. A chronically implanted monitor that provides early warnings of heart attacks could greatly reduce time to treatment, which in turn will dramatically decrease heart-attack related deaths and improve the quality of life of heart attack survivors. This monitor will be an important health care advance since coronary heart disease is the top cause of death in the U.S. and one of the leading costs to the healthcare system. This Phase II research builds upon our successful Phase I work, which entailed the development and evaluation of an ischemia detection algorithm using a small patient population. This Phase II project will result in the creation of a monitor that is ready for a clinical safety trial. This goal will be realized by achieving the following aims: Aim 1. Demonstrate the efficacy of an algorithm that will run within an implantable device that utilizes two subcutaneous vectors. In this aim, we will evaluate and refine the Phase I algorithm by testing it on two datasets. The first dataset will include Holter recordings from a control group of 36 high-risk individuals who will be monitored for approximately 2 weeks (no ischemia detections should occur in this group). The second dataset will include 24-hour, 12- lead recordings from hundreds of cases of confirmed AMIs. Aim 2 Demonstrate the functionality of the entire monitoring system, including the implantable device, the physician's programmer that remotely programs the implantable device in situ, and the subcutaneous lead. To further the achievement of this aim, the algorithm will be implemented within a new implantable hardware platform. Successful completion of this aim will be shown when the entire system passes all tests required to obtain United States Food and Drug Administration approval for a clinical safety trial.